HARRISBURG — Fewer and fewer Pennsylvania school districts are seeking approval to raise property taxes beyond a state-imposed inflation index without voter approval. A state Department of Education report released today shows 171 of the 497 districts in the report were granted exceptions from a requirement that local voters approve tax increases that exceed the index. Officials say this is the third straight year in which those requests have declined. Department spokesman Tim Eller speculated that the trend reflects boards’ reluctance to raise taxes and more innovative methods for holding down expenses. Of the remaining districts, 311 approved resolutions declaring they would not increase taxes above the index, and 15 others left open the possibility that they would seek voter approval for larger increases in the May 21 primary.